Method for producing aramid laminate

ABSTRACT

A process for preparing an aramid laminate, which comprises impregnating a surface and an interior an aramid paper with a liquid crystal polymer, and laminating a layer comprising an aramid paper and a layer comprising a liquid crystal polymer.

TECHNICAL FIELD

The present invention relates to an aramid laminate used insulator suchas in a motor, transformer, or electric•electronic circuit substratessuch as printed circuit board.

BACKGROUND TECHNIQUE

Since an aramid paper is excellent in heat resistance, it is widely usedin utility such as insulator, and substrates such as printed circuitboards and, for example, as an insulating material using an aramidpaper, an aramid laminate in which an aramid paper and a polyethyleneterephthalate (hereinafter referred to as “PET”) film are laminated andintegrated is proposed (JP-A No. 7-32549).

However, when the aramid laminate is exposed to a high temperature by astep of solder reflow and the like, deformation such as warpage occursin the aramid laminate in some cases since PET itself is inferior insolder heat resistance.

In addition, as a substrate of a printed curcuit board using an aramidpaper, an aramid laminate in which an aramid paper and a thermosettingresin are combined is proposed (JP-A No. 2000-141522).

However, since a thermosetting resin has a large moisture absorptionrate, electric reliability of electronic parts packaged on the printedcircuit board is decreased due to operating environment such as atemperature and a humidity in some cases.

On the other hand, as an example on a heat resistant material other thanan aramid paper used in utility of a substrate, a laminate using a heatresistant liquid crystal polymer film as a substrate of a printedcircuit board is proposed (JP-A No. 08-323923).

However, since a liquid crystal polymer has anisotropy, and an expansionrate of a printed circuit board is different every direction of thecircuit board due to anisotropy of a liquid crystal polymer, in thefield requiring a further finer circuit wiring, procession of a circuitwiring becomes further difficult, and it may be difficult to suppressbreakage of a circuit wiring due to thermal expansion of the circuitboard in some cases.

An object of the present invention is to provide a process for preparingan aramid laminate excellent in solder heat resistance and lowhygroscopicity.

DISCLOSURE OF THE INVENTION

In order to solve the aforementioned problems, the present inventorsintensively studied and, as a result, found out that, by laminating eachat least one layer of a layer composed of an aramid paper and a layercomposed of a liquid crystal polymer, an aramid laminate excellent insolder heat resistance and low hygroscopicity is obtained, whichresulted in completion of the present invention.

That is, the present invention relates to:

a process for preparing an aramid laminate which comprises a step oflaminating a layer comprising an aramid paper and a layer comprising aliquid crystal polymer by impregnating a surface and an interior of anaramid paper with a liquid crystal polymer, and penetrating the liquidcrystal polymer into the aramid paper, or

a process for preparing an aramid laminate which comprises a step ofthermally fusing a layer comprising an aramid paper and a layercomprising a liquid crystal polymer at a temperature range of from atemperature lower than a flowing temperature of a liquid crystal polymerby 30° C. to lower than 400° C. at a planar pressure of 10 kg/cm² orhigher, or at a linear pressure of 20 kg/cm or higher, and relates to acircuit substrate comprising the aramid laminate obtained by the processany of the aforementioned processes.

PREFERABLE MODE FOR CARRYING OUT THE INVENTION

The present invention will be explained below.

An aramid paper used in the present invention will be explained.

The aramid paper of the present invention is a heat resistant papercomposed of an aramid fibrid, an armid short fiber and the like, and isgenerally prepared by a process of making a paper by a wet format fromthese aramid fibrid, aramid short fiber and the like. The “fibrid” is acoined word by DuPont and means a fine fibrous material havingpapermaking property.

An aramid paper is generally a paper of a fibrid or a short fibercomposed of wholly aromatic aramid such as p-aramid and m-aramid alone,or a paper of an appropriate combination of them.

Herein, p-aramid is an alternate copolymer of an aromatic diamine, asrepresented by 1,4-diaminobenzene and 4,4′-diaminodiphenyl ether inwhich two amino groups in a molecule substitute at para positions of abenzene ring with each other, and aromatic dicarboxylic acids, asrepresented by terephthalatic acid in which two carboxyl groups in amolecule substitute at para positions of a benzene ring with each other,and has an amide bond structure in which an amino group and a carboxylgroup are mutually condensed. Example of such the p-aramid includepoly(p-phenyleneterephthalamide), andpoly(p-diphenyletherterephthalamide). In addition, m-aramid has the samemolecular structure except that a binding relation of the p-aramid inchanged from a para position to a meta position, and examples includepoly(m-phenyleneisophthalamide).

A process for preparing an aramid fibrid is not limited, butspecifically, an aramid fibrid can be obtained by wet precipitation of asolution containing aramid, for example, a sulfuric acid solution, andan organic solution such as NMP. In addition, a process for preparing anaramid paper is not particularly limited, but examples include a methodof dispersing the fibrid or the aramid short fiber in an aqueoussolution to the diluted slurry state of around 0.01 to 1.0% by weight,converting this to a web with a paper making machine and, thereafter,obtaining an aramid paper via a water squeezing step and a drying step.When this aramid paper is made, if necessary, a fiber or a pulp of otherheat resistance resin may be blended. Specifically, for example, a fiberor a pulp of a liquid crystal polymer containing a wholly aromaticpolyester, or super engineering plastics such as aromatic polyetherether ketone (PEEK) may be blended. In addition, if necessary, bysubjecting an aramid paper to calendaring procession, necessarymechanical property may be imparted to an aramid paper, or a thicknessor a density thereof may be adjusted.

A layer composed of a liquid crystal polymer can be laminated on a layercomposed of an aramid paper by the aforementioned method and a processfor preparing an aramid laminate such as provision of a layer composedof a liquid crystal polymer on a metal layer can be performed by thesame method as the aforementioned method.

Upon preparation of an aramid laminate, an aramid laminate may beprepared by a stepwise process of laminating one layer by one layer, oran aramid laminate may be prepared by a process of laminating respectivelayers at once by a method of thermal pressing or thermal roll.

A liquid crystal polymer used in the present invention is a polymerexhibiting optical anisotropy at melting, which is called thermotropicliquid crystal polymer. Examples of such the liquid crystal polymerinclude wholly aromatic polyester containing no aliphatic carbon on apolymer chain, liquid crystal polyesters such as aromatic polyestercontaining an aliphatic carbon on a polymer chain, liquid crystal imidessuch as polyester imide, liquid crystal amides such as polyester amides,and resin compositions containing them. Preferable are liquid crystalpolyesters and resin compositions containing them, and furtherpreferable are wholly aromatic liquid crystal polyester and resincompositions containing it.

Specific examples of a liquid crystal polymer as represented by liquidcrystal polyester include:

1) A liquid crystal polymer composed of a combination of a repeatingunit derived from aromatic dicarboxylic acid, a repeating unit derivedfrom aromatic diol, and a repeating unit derived from aromatichydroxycarboxylic acid,

2) A liquid crystal polymer composed of a combination of repeating unitsderived from different aromatic hydroxycarboxylic acids,

3) A liquid crystal polymer composed of a combination of a repeatingunit derived from aromatic dicarboxylic acid and a repeating unitderived from aromatic diol, and

4) A liquid crystal polymer obtained by reacting polyester such aspolyethylene terephthalate with aromatic hydroxycarboxylic acid.

These usually form an anisotropic molten state at a temperature of 400°C. or lower. It is preferable that liquid crystal polyester composed ofeach combination of the 1) to 3) is wholly aromatic liquid crystalpolyester. In addition, in place of aromatic dicarboxylic acid, aromaticdiol and aromatic hydroxycarboxylic acid used in preparation of theliquid crystal polyester, an ester forming derivative thereof may beused. Further, instead of these aromatic dicarboxylic acid, aromaticdiol and aromatic hydroxylcarboxylic acid, a compound in which anaromatic nucleus is substituted with a halogen atom, an alkyl group, oran aryl group. Examples of a repeating unit include the following units.

(I) The following repeating unit derived from aromatic dicarboxylicacid:

A hydrogen atom of a benzene ring in each structure may be substiutedwith a halogen atom, an alkyl group, or an aryl group.

A hydrogen atom of a benzene ring in each structure may be substiutedwith a halogen atom, an alkyl group, or an aryl group.

II) The following repeating unit derived from aromatic diol:

A hydrogen atom of a benzene ring in each structure may be substitutedwith a halogen atom, an alkyl group, or an aryl group.

A hydrogen atom of a benzene ring in each structure may be substitutedwith a halogen atom, an alky; group, or an aryl group.

III) The following repeating unit derived from aromatichydroxycarboxylic acid:

A hydrogen atom of a benzene ring in each structure may be substitutedwith a halogen atom, an alkyl group, or an aryl group.

From a viewpoint of balance between heat resistance, mechanical propertyand processibility, particularly preferable liquid crystal polyestercontains a repeating unit of:

and further preferably contains the repeating unit at least 30 mol % ormore of a whole. A liquid crystal polyester having any one of repeatingunit combinations of the following (I) to (VI) is preferable. As thefollowing liquid crystal polyester, liquid crystal polyesters in whichan aromatic ring is substituted with a halogen group, an alkyl group, oran aryl group can be used.

A process for preparing the liquid crystal polyesters (I) to (VI) isdescribed, for example, in JP-B No. 47-47870, JP-B No. 63-3888, JP-B No.63-3891, JP-B No. 56-18016, and JP-A No. 2-51523. Among them, preferableare a combination of (I) or (II) or (VI), and further preferable are acombination of (I) or (II).

In the field requiring particularly high heat resistance, a liquidcrystal polyester containing 30 to 80 mol % of the following repeatingunit (a′), 0 to 10 mol % of the following repeating unit (b′), 10 to 25mol % of the following repeating unit (c′), and 10 to 35 mol % of therepeating unit (d′) is preferably used.

(wherein Ar is a divalent aromatic group, and the aforementionedaromatic ring of the (a′) to (d′) substituted with a halogen group, analkyl group, or an aryl group may be used)

As the repeating unit (d′), the aforementioned diol is preferable and,in utility requiring particularly high heat resistance, wholly aromaticdiol is preferable.

As a liquid crystal polyester to be used, a liquid crystal polyester ofa combination of only carbon, hydrogen and oxygen is preferably usedfrom a viewpoint of easy waste by incineration after use.

As a layer composed of a liquid crystal polymer, a liquid crystalpolymer film can be used and, from a viewpoint of such the moldabilitythat such the liquid crystal polymer film is stably used, it is furtherpreferable to use, as the liquid crystal polymer, a liquid crystalpolyester resin composition containing (A) liquid crystal polyester as acontinuous phase, and (B) a copolymer having a functional group havingreactivity with liquid crystal polyester as a dispersion phase.

As the component (B) used in the liquid crystal polyester resincomposition, a copolymer having a functional group having reactivitywith liquid crystal polyester is preferable. Examples of such thefunctional group having reactivity with a liquid crystal polyesterinclude an oxazolyl group, an epoxy group and an amino group. Preferableis an epoxy group.

An epoxy group and the like may be present as a part of other functionalgroup, and examples include a glycidyl group.

In a copolymer (B), a method of introducing a functional group havingreactivity with a liquid crystal polymer such as liquid crystalpolyester into the copolymer is not particularly limited, butintroduction can be performed by known methods. For example, it ispossible to introduce a monomer having the functional group bycopolymerization at a stage of synthesizing a copolymer or it ispossible to graft-copolymerize the copolymer with a monomer having thefunctional group.

A copolymer (B) may be a thermoplastic resin or a rubber, or a mixtureor a reaction product of a thermoplastic resin and a rubber. When heatstability and flexibility of a molded article such as a film and a sheetobtained using a liquid crystal polymer resin composition are consideredimportant, a rubber can be selected.

When a copolymer (B) is a rubber, examples of a copolymer having afunctional group having reactivity with a liquid crystal polymer such asa liquid crystal polyester include a rubber having an epoxy group suchas a (meth)acrylic acid ester-ethylene-(unsaturated carboxylic acidglycidyl ester and/or unsaturated glycidyl ether) copolymer rubber.

Herein, (meth)acrylic acid ester means esters obtained from acrylic acidor methacrylic aicd and alcohols. Examples of alcohols include hydroxylgroup-containing compounds having a carbon number of 1 to 8. Examples of(meth)acrylic acid ester include methyl acrylate, methyl methacrylate,n-butyl acrylate, n-butyl methacrylate, tert-butyl acrylate, tert-butylmethacrylate, 2-ehtylhexyl acylate and 2-ethylhexyl methacrylate. As the(meth)acrylic acid ester, one kind thereof may be used alone or two ormore kinds may be used together.

Examples of unsaturated carboxylic acid glycidyl ester and unsaturatedglycidyl ether include the following general formula:

(wherein R represents a hydrocarbon group of a carbon number of 2 to 13having an ethylenic unsaturated bond, and X represents —C(O)—, —CH₂—O—or

Examples of unsaturated carboxylic acid glycidyl ester include glycidylacrylate, glycidyl methacylate, itaconic acid diglycidyl ester,butenetricarboxylic acid triglycidyl ester, and p-styrene carboxylicacid glycidyl ester.

Examples of unsaturated glycidyl ether include vinyl glycidyl ether,allyl glycidyl ether, 2-methylallylglycidyl ether, methacryl glycidylether, and styrene-p-glycidyl ether.

Among the aforementioned copolymer rubber, a content of a (meth)acrylicacid ester monomer unit in a copolymer is preferably in a range of 40 to97% by weight, further preferably 45 to 70% by weight.

A content of an ethylene monomer unit is preferably in a range of 3 to50% by weight, further preferably in a range of 10 to 49% by weight. Acontent of an unsaturated carboxylic acid glycidyl ether monomer unitand/or an unsaturated glycidyl ether monomer unit is preferably in arange of 0.1 to 30% by weight, more preferably in a range of 0.5 to 20%by weight.

The copolymer rubber can be prepared by a conventional method such asbulk polymerization, emulsion polymerization, and solutionpolymerization using a free radical initiator. A representativepolymerization method is a method described in JP-B No. 48-11388 or JP-ANo. 61-127709, and the rubber can be prepared in the presence of a freeradical generating polymerization initiator under condition of apressure of 500 kg/cm²(49.0 MPa) or higher, and a temperature of 40 to300° C.

In addition to the aforementioned rubbers, an acryl rubber having afunctional group having reactivity with liquid crystal polyester, or ablock copolymer rubber of a vinyl aromatic hydrocarbon compound having afunctional group having reactivity with liquid crystal polyester andconjugated diene compound can be also used.

Examples of a monomer of an acryl rubber referred herein includemonomers represented by the general formulas (1) to (3):CH₂═CH—C(O)—OR¹   (1)CH₂═CH—C(O)—OR²OR³   (2)CH₂═CR⁴—C(O)—O(R⁵(C(O)O)_(n)R⁶   (3)(wherein R¹ represents an alkyl group of a carbon number of 1 to 18 or acyanoalkyl group of a carbon number of 1 to 18, R² is an alkylene groupof a carbon number of 1 to 12, R³ represents an alkyl group of a carbonnumber of 1 to 12, R⁴ represents a hydrogen atom or a methyl group, R⁵represents an alkylene group of a carbon number of 3 to 30, R⁶represents an alkyl group of a carbon number of 1 to 20 or a derivativethereof, and n represents an integer of 1 to 20)

A constitutional component ratio of an acryl rubber having a functionalgroup having reactivity with a liquid crystal polymer, represented byliquid crystal polyester, is usually that at least one kind monomerselected from monomers represented by the general formulas (1) to (3) is40 to 99.9% by weight, unsaturated carboxylic acid glycidyl ester and/orunsaturated glycidyl ether is 0.1 to 30% by weight, and an unsaturatedmonomer copolymerizable with monomers represented by the generalformulas (1) to (3) is 0 to 30% by weight.

Examples of acrylic acid alkyl ester represented by the general formula(1) include methyl acrylate, ethyl acrylate, propyl acrylate, butylacrylate, pentyl acrylate, hexyl acylate, octyl acrylate, 2-ethylhexylacrylate, nonyl acrylate, decyl acrylate, dodecyl acrylate, andcyanoethyl acrylate. These one or two or more kinds can be used as amain component of the acryl rubber.

In addition, examples of acrylic acid alkoxyalkyl ester represented bythe general formula (2) include methoxyethyl acrylate, ethoxyethylacrylate, butoxyethyl acrylate, and ethoxyethyl acrylate. These one ortwo or more kinds can be used as a main component of the acryl rubber.

Examples of the acrylic acid derivative represented by the generalformula (3) include acryloyloxy-butyric methyl ester, andmethacryloxy-heptanoic acid methyl ester. These one or two or more kindscan be used as a main component of the acryl rubber.

As a constitutional component of an acryl rubber, an unsaturated monomercopolymerizable with monomers represented by the general formulas (1) to(3) can be used, if necessary.

Examples of such the unsaturated monomer include styrene,α-methylstyrene, acrylonitrile, halogenated styrene, methacrylonitrile,acrylamide, methacrylamide, vinylnaphthalene, N-methylolacrylamide,vinyl acetate, vinyl chloride, vinylidene chloride, benzyl acrylate,methacrylic acid, itaconic acid, fumaric acid, and maleic acid.

A process for preparing the acryl rubber is not particularly limited,but for example, the known polymerization method described, for example,in JP-A No. 59-113010, JP-A No. 62-64809, JP-A No. 3-160008, andWO95/04764 can be used, and the acryl rubber can be prepared by emulsionpolymerization, suspension polymerization, solution polymerization orbulk polymerization in the presence of a radical initiator.

In addition to the acryl rubber, examples of a block copolymer of thevinyl aromatic hydrocarbon compound having a functional group havingreactivity with liquid crystal polyester and conjugated diene compoundinclude a rubber obtained by epoxylating a block copolymer composed of(a) a sequence mainly containing a vinyl aromatic hydrocarbon compoundand (b) a sequence containing mainly a conjugated diene compound, and arubber obtained by epoxylating a hydrogenated material of the blockcopolymer.

Examples of the (a) vinyl aromatic hydrocarbon compound include styrene,vinyltoluene, divinylbenzene, α-methylstyrene, p-methylstyrene, andvinylnaphthalene. Inter aria, styrene is preferable.

Examples of the (b) conjugated diene compound include butadiene,isoprene, 1,3-pentadiene, and3-butyl-1,3-oxtadiene. Butadiene orisoprene is preferable.

Such the block copolymer of vinyl aromatic hydrocarboncompound-conjugated diene compound or a hydrogenated product thereof canbe prepared by the known process, and the process is described, forexample, in JP-B No. 40-23798, and JP-A No. 59-133203.

A rubber used as the copolymer (B) is vulcanized as necessary, and canbe used as a vulcanized rubber.

Vulcanization of the copolymer rubber of the (meth) acrylic acidester-ethylene-(unsaturated carboxylic acid glycidyl ester and/orunsaturated glycidyl ether) is attained by using a polyfunctionalorganic acid, a polyfunctinal amine compound, or an imidazole compound,being not limiting.

When the copolymer (B) is a thermoplastic resin other than a rubber, forexample,

(a) ethylene,

(b) unsaturated carboxylic acid glycidyl ester monomer and/orunsaturated glycidyl ether monomer,

(c) ethylenic unsaturated ester compound;

Examples include epoxy group-containing ethylene copolymers obtained byreacting the above (a) and (b), or (a), (b) and (c). Inter alia, it ispreferable that an ethylene unit in a copolymer is in a range of 50 to99% by weight, and unsaturated carboxylic acid glycidyl ester monomerunit and/or an unsaturated glycidyl ether monomer unit is in a range of0.1 to 30% by weight, and an ethylene unsaturated ester compound unit isin a range of 0 to 50% by weight. Further, among them, it is furtherpreferable that a range of an unsaturated carboxylic acid glycidyl estermonomer unit and/or an unsaturated glycidyl ether monomer unit is 0.5 to20% by weight.

Examples of the ethylene unsaturated ester compound (c) includecarboxylic acid vinyl ester such as vinyl acetate, vinyl propionate,methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate,ethyl methacrylate, and butyl methacrylate and α,β-unsaturatedcarboxylic acid alkyl ester. Inter alia, vinyl acetate, methyl acrylate,and ethyl acrylate are preferable.

Examples of the epoxy group-containing ethylene copolymer include acopolymer of an ethylene unit and a glycidyl methacrylate unit, acopolymer of an ethylene unit, a glycidyl methacrylate unit and a methylacrylate unit, a copolymer of an ethylene unit, a glycidyl methacrylateunit and an ethyl acrylate unit, and a copolymer of an ethylene unit, aglycidyl methacrylate unit and a vinyl acetate unit.

A melt flow rate (hereinafter, referred to as MFR in some cases, JISK7210, 190° C., 2.16 kg load) of the epoxy group-containing ethylenecopolymer is preferably 0.5 to 100 g/10 min, further preferably 2 to 50g/10 min. A melt flow rate may be outside this range, but when a meltflow rate exceeds 100 g/10 min, this may not be preferable in mechanicalproperty when formulated into a composition and, when a melt flow rateis less than 0.5 g/10 min, compatibility with a liquid crystal polymer,such as liquid crystal polyester, of a component (A) may not besuperior, being not preferable.

In addition, regarding the epoxy group-containing ethylene copolymer, acopolymer having a flexural modulus in a range of 10 to 1300 kg/cm²(0.98 to 127.49 MPa) may be selected, but 20 to 1100 kg/cm² (1.96 to107.87 MPa) is further preferable.

The epoxy group-containing ethylene copolymer is usually prepared by ahigh pressure radical polymerization method in which an unsaturatedepoxy compound and ethylene are copolymerized at 100 to 300° C. under apressure of 500 to 4000 atm in the presence or the absence of a suitablesolvent and a chain transfer agent in the presence of a radicalgenerator. Alternatively, the epoxy group-containing ethylene copolymercan be also prepared by a method of mixing a polyethylene with anunsaturated epoxy compound and a radical generator, and subjecting themixture to melt graft copolymerization in an extruder.

As the copolymer (B), a copolymer in which 0.1 to 30% by weight of anunsaturated carboxylic acid glycidyl ester monomer unit and/or anunsaturated glycidyl ether monomer unit is contained in the copolymer,is preferably used.

It is preferable to use the copolymer (B) having a crystal melting heatamount of less than 3J/g.

A Mooney viscosity is preferably 3 to 70, more preferably 3 to 30, andparticularly preferably 4 to 25.

As used herein, a Mooney viscosity refers to a value measured using a100° C. large rotor according to JIS K6300. When the viscosity isoutside the range, there is a tendency that a heat stability of thecomposition is reduced.

The copolymer (B) to be used is preferably a copolymer of a combinationof only carbon, hydrogen and oxygen, from a viewpoint of easy waste byincineration after use.

Examples of a liquid crystal polyester resin composition used in thepresent invention include a resin composition comprising (A) 56.0 to99.9% by weight, preferably 70.0 to 99.9% by weight, further preferably80 to 98% by weight of liquid crystal polyester, and (B) 44.0 to 0.1% byweight, preferably 30.0 to 0.1% by weight, further preferably 20 to 2%by weight of a copolymer having a functional group having reactivitywith a liquid crystal polyester.

A film containing (B) a copolymer having a functional group havingreactivity with a liquid crystal polyester is more preferable sinceadherability to an aramid paper is improved.

As a process for preparing a liquid crystal polyester resin compositioncontaining a liquid crystal polyester (A) and a copolymer (B), theconventional method can be used. Examples include a method of mixingeach component in the solution state, and evaporating a solvent, orprecipitating the composition in a solvent. Specifically, a method ofkneading each component in the melted state can be selected. For meltkneading, a kneading apparatus such as a monoaxial or biaxial extruder,and various kneaders which are generally used can be used. Inparticular, a biaxial high kneading machine is preferable.

Upon melt kneading, a set temperature of a cylinder of a kneadingapparatus can be selected from a range of 200 to 360° C., and it ispossible to implement melt kneading in a range of 230 to 350° C.

Upon kneading, respective components may be uniformly mixed with anapparatus such as a tumbler and a Henschel mixer in advance, or ifnecessary, mixing is omitted, and a method of quantitatively supplyingrespective components to a kneading apparatus separately.

If necessary, various additives such as an organic filler, anantioxidant, a heat stabilizer, a light stabilizer, a flame-retardant,lubricant, an antistatic agent, a rust-proofing agent, a crosslinkingagent, a foaming agent, a fluorescent agent, a surface smoothing agent,a surface lust improving agent, and a release improving agent such as afluorine resin can be added to a liquid crystal polyester resincomposition during a preparing step or at a processing step thereafter,and it is preferable to use additives other than a halogen or additiveswhich do not leave an ash after combustion.

A process for preparing the aramid laminate of the present invention isa process of immersing an interior of the layer comprising an aramidpaper with the liquid crystal polymer or a composition thereof, andlaminating a layer comprising an aramid paper and a layer containing aliquid crystal polymer. Specifically, examples include a method ofspraying or adhering a powder of a liquid crystal polymer to a surfaceof a layer comprising an aramid layer, followed by impregnating aninterior of an aramid paper by heating to melt the powder, a method ofcoating a liquid crystal polymer dissolved in the solvent to an aramidpaper to enter an interior of an aramid, followed by drying a solvent,and a method of overlaying a molded film containing a liquid crystalpolymer (hereinafter, referred to as “liquid crystal polymer film”) onan aramid paper, and thermally fusing them, followed by impregnationinto an interior of an aramid paper. From a viewpoint of processibilityand workability of application and the like, a method of overlaying aliquid crystal polymer film on an aramid paper, and thermally fusingthem is preferable.

Examples of the method of overlaying a liquid crystal polymer film on anaramid paper, and thermally fusing them include a method of performingthermal fusing with a thermal press and a thermal roll.

By such the thermal fusing method, voids of an aramid paper areimpregnated with a liquid crystal polymer, and a surface and an interiorof an aramid paper are impregnated with a liquid crystal polymer,thereby, a layer comprising an aramid paper and a layer comprising aliquid crystal polymer are laminated. As a result, since adherabilitybetween a liquid crystal polymer and an aramid paper can be furtherenhanced, it is preferable to perform thermal fusing with a thermalpress or a thermal roll. A liquid crystal polymer may be impregnatedinto an entire interior of an aramid paper, or may be impregnated into apart of the interior.

A temperature range upon thermal fusing is usually from a temperaturelower than a flowing temperature of a liquid crystal polymer by 30° C.to lower than 400° C. When a heating temperature is further lower thantemperature lower than a flowing temperature of a liquid crystal polymerby 30° C., a liquid crystal polymer is not sufficiently melted in somecases. In addition, at a temperature of 400° C. or higher, a part of aliquid crystal polymer is thermally degraded in some cases.

A pressure when a crystal liquid polymer film and an aramid paper arethermally fused is usually set at 10 kg/cm² or higher as expressed by aplanar pressure in the case of use of a thermal press. A linear pressureis usually set at 20 kg/cm or higher in the case of use of a thermalroll.

Herein, a flowing temperature (FT) refers to a temperature (° C.) atwhich a melt viscosity measured with a capillary-type rheometer exhibits48,000 poise, when a resin which has been heated and melted at atemperature raising rate of 4° C./min is extruded through a nozzle of aninner diameter of 1 mm and a length of 10 mm under a load of 100kgf/cm².

Examples of a method of molding a liquid crystal polymer film include amethod of obtaining a film from a solution in which a liquid crystalpolymer is dissolved in a solvent, by a casting method, a method ofmolding into a film by a thermal press, and a molding method using a Tdie or an inflation die.

Inter alia, a T die method of extruding a melt resin through a T die andwinding a film, an inflation molding method of extruding a melt resininto a cylinder shape from an extruder in which a circular die isarranged, and cooling and winding a film, a thermal pressing method, anda molding method using a calendar or a roll are preferably used, andfurther preferable is a T die method, and a more preferable is aninflation molding method.

In inflation molding, a liquid crystal polyester composition containingthe (A) liquid crystal polyester and the (B) copolymer having afunctional group having reactivity with liquid crystal polyester ispreferably used. More preferably, a blowing ratio (a stretching ratio ina direction orthogonal with a resin flowing direction (TD)) is not lessthan 1.5 and less than 10, and a drawing down ratio (a stretching ratioin a resin flowing direction (MD)) is 1.5 to 50.

When a setting condition at inflation molding is outside theaforementioned range, it may become difficult to obtain a film having auniform thickness, no crease and a high strength in some cases. That is,when a blowing ratio is less than 1.5, a strength in a TD direction ofthe resulting film is not sufficient in some cases, being notpreferable. In addition, a blowing ratio is not less than 10, a filmhaving a stable thickness may not be obtained in some cases, being notpreferable. In addition, when a drawing ratio is less than 1.5, astrength in a MD direction of the resulting film may not be sufficientin some cases, being not preferable. In addition, when a drawing downratio is not less than 50, a film having a stable thickness may not beobtained in some cases, being not preferable.

A thickness of a liquid crystal polymer film is not particularlylimited, is appropriately determined by a thickness of an aramid paper,and a finally required thickness of an aramide laminate, and is usuallyin a range of not less than 0.5 μm and not more than 2 mm, preferablynot less than 5 μn and not more than 500 μm.

A normally used heat resistant temperature of a liquid crystal polymerto be used is usually 140° C. or higher, preferably 160° C. or higher.Herein, a normally used heat resistant temperature indicates atemperature at which a time necessary for reduction in a MD directiontensile breakage strength by ½ is 40,000 hours. Further, a solder heatresistance temperature of the liquid crystal polymer is usually 250° C.or higher, preferably 280° C. or higher. Herein, a solder heat resistanttemperature indicates an upper limit temperature at which a film isimmersed in a heated solder bath for 10 seconds, and no foaming due toshrinkage or thermal degradation is perceived.

A water steam permeability of a liquid crystal polymer is usually 1.0g/m²·24 hr or lower, preferably 0.8 g/m²·24 hr or lower. When a watersteam permeability is great, there is a possibility that waterabsorption of an araimd laminate obtained after lamination of an aramidpaper may become great, being not preferable. A water absorption rate ispreferably less than 0.2%, further preferably 0.1%. When a waterabsorption rate is great, upon use of an aramid laminate as a circuitboard, deteriorated application to a copper foil at procession may occurin some cases, being not preferable.

A surface free energy of a liquid crystal polymer is preferably 35dyne/cm or more. When the energy is less than that value, unevenness ofapplication to an aramid paper may occur and, when the resulting aramidlaminate is adhered to a coated board, a resin, a metal, or a timber,there may be a possibility that a laminate is peeled during long termuse, being not preferable. When a surface free energy of a liquidcrystal polymer such as a liquid crystal polymer film is less than 35dyne/cm, surface treatment such as corona treatment may be performed.

A metal layer may be further laminated on an aramid laminate obtainedabove.

A metal used in a metal layer may be a conductor metal such as gold,silver, copper and iron and, usually, copper is used. Examples of amethod of forming a metal layer include a method of forming a layerusing a metal foil, and a method of forming a layer on a layercomprising an aramid paper or a layer comprising a liquid crystalpolymer by metal plating or metal deposition. As a metal foil, a rolledfoil or an electrolytic foil is usually used. Metal plating may beelectrolytic plating or non-electrolytic plating. Further, another layermay be laminated on a metal layer, and a wiring circuit pattern may beformed in advance on a metal layer by performing etching treatment on ametal foil. When an aramid laminate is “a laminate containing each atleast one layer of a layer comprising an aramid paper and a layercomprising a liquid crystal polymer”, examples of such the aramidlaminate include a three-layered aramid laminate containing each layerin an order of (i) to (iii) such as (i) a layer comprising a liquidcrystal polymer, (ii) a layer comprising an aramid paper and (iii) aliquid crystal polymer. The aramid laminate is not limited to an exampleof the aforementioned three-layered aramid laminate, and a laminatingorder of each layer, and a laminating number can be arbitrarily set.

When an aramid laminate is “a laminate containing each at least onelayer of a layer comprising an aramid layer, a layer comprising a liquidcrystal polymer and a metal layer”, examples of such the aramid laminateinclude a four-layered aramid laminate containing each layer in an orderof (i) to (iv) such as (i) a metal layer, (ii) a layer comprising aliquid crystal polymer, (iii) a layer comprising an aramid paper and(iv) a layer comprising a liquid crystal polymer, and a five-layeredaramid laminate containing each layer in an order of (i) to (v) such as(i) a metal layer, (ii) a layer comprising a liquid crystal polymer,(iii) a layer comprising an aramid paper, (iv) a layer comprising aliquid crystal layer and (v) a metal layer. These aramid laminatescontaining a metal layer are not limited to an example of theaforementioned four to five-layered aramid-laminates, and a laminationorder of each layer and a lamination number can be arbitrarily set, butan aramid laminate has preferably a construct containing a laminatestructure in which a layer comprising an aramid paper is held between alayer comprising a liquid crystal polymer and a layer comprising aliquid crystal polymer, from a viewpoint of reduction in waterabsorption. An aramid laminate containing a metal layer on which awiring circuit pattern is formed can be suitably used as a circuitsubstrate.

EXAMPLE 1

The present invention will be explained in detail by way of Examples,but the present invention is not limited to only Examples. Each physicalproperty is measured by following method.

[Method of Measuring Physical Property]

Flowing temperature (FT): this is an index for showing melt flowability,and was measured with a capillary-type rheometer (Elevation-type flowtester CFT500 type manufactured by Shimadzu Corporation), and a flowingtemperature was expressed as a temperature (° C.) at which a meltviscosity shows 48,000 poise when a sample resin (about 2 g) which hasbeen heated and melted at a temperature raising rate of 4° C./min isextruded through a nozzle of an internal diameter 1 mm and a length 10mm under a load of 100 kg/cm².

Optical anisotropy: optical anisotropy of a sample resin in the meltstate was confirmed by raising a temperature of a sample resin powder ofa particle diameter of 250 μm or smaller placed on a heating stage at25° C./min under polarization, and observing with naked eyes orrecording an amount of transmitted light with a XY recorder.

Method of measuring heat resistance of film:

<Normally Used Heat Resistant Temperature>

A film was placed in a hot air oven retained at 50° C., 100° C., 150°C., 200° C., or 250° C., the film was taken out every 500 hours from 0hour to 2500 hours, allowed to stand in a constant temperature constanthumidity chamber (23° C., 55% RH) for one day, and a tensile strength ina MD direction was measured to obtain a time dependent curve of astrength. Therefrom, a time at which a strength becomes a half ofstrength at 0 hour was obtained every temperature, the resulting time(reduction by half time) was plotted against a temperature to obtain acurve, and a temperature in the case where reduction by half time was40,000 hours was adopted as a normally used heat resistance temperature.A tensile strength of a film was according to JIS C2318.

<Solder Heat Resistance Temperature>

A solder heat resistance temperature was assessed by an upper limittemperature at which a film was immersed in a heated solder bath for 10seconds, and no foaming due to shrinkage and thermal degradation wasperceived.

Method of measuring water steam permeability and water absorption rateof film:

<Water Steam Permeability>

A water steam permeability was measured at a temperature of 40° C. and arelative humidity of 90% according to JIS Z0208 (cup method). A unit isg/m²·24 hr.

A water steam permeability is not converted by a film thickness.

<Moisture Absorption Rate>

Letting a mass of a substrate film after heating and drying at 120° C.for 2 hours in a hot air oven to be A, and a mass after 24 hours fromallowing to stand of the film in a chamber retained at a constanttemperature and a constant humidity, which was adjusted to 20° C. and70% RH to be B, a moisture absorption rate was measured by the followingequation.Moisture absorption rate (%)={(B−A)/B}=100<Coefficient of Thermal Expansion>

A Coefficient of thermal expansion was measured using a thermal analysisapparatus TMA120 manufactured by Seiko Electronics, and was calculatedby the following equation, according to ASTM D696.α1=ΔL/L ₀ ·ΔTwherein α1: Coefficient of thermal expansion(/° C.)

ΔL: change length of test piece

L₀: test piece length before test

ΔT: temperature difference (° C.)

Assessment of surface free energy of support substrate film:

According to JIS K6768, a standard solution was coated, followed bydetermination:

REFERENCE EXAMPLE

(1) Liquid crystal polymer exhibiting optical anisotropy at melting

(1-1) (A) Liquid crystal polyester constituting liquid crystal polymerexhibiting optical anisotropy at melting.

A polymerization vessel having a comb-type stirring wing was chargedwith 8.3 kg (60 mol) of p-acetoxybenzoic acid, 2,49 kg (15 mol) ofterephthalic acid, 0.83 kg (5 mol) of isopthalic acid and 5.45 kg (20.2mol) of 4,4′-diacetoxydiphenyl, a temperature was raised while stirringunder the nitrogen gas atmosphere, and polymerization was performed at330° C. for 1 hour. Polymerization was performed under strong stirring,while an acetic acid gas produced as a by product during that time wasliquefied with a cooling tube, recovered and removed. Thereafter, thesystem was gradually cooled, and a polymer obtained at 200° C. was takenout from the system. This resulting polymer was ground to a particle of2.5 mm or smaller with a hammer mill manufactured by Hosokawa MicronCorporation. This was further treated at 280° C. for 3 hours under thenitrogen gas atmosphere in a rotary kiln, to obtain a particulate whollyaromatic polyester consisting of the following repeating structural unithaving a flowing initiating temperature of 327° C.

Herein, the following initiating temperature refers to a temperature (°C.) at which a melt viscosity shows 48000 poise when a resin which hasbeen heated and melted at a temperature raising rate of 4° C./min isextruded through a nozzle of an internal diameter of 1 mm and a lengthof 10 mm under a load of 100 kgf/cm², using a Shimadzu flow testerCFT-500 type manufactured by Shimadzu Corporation.

Hereinafter, the liquid crystal polyester is abbreviated as A-1. Thispolymer showed optical anisotropy at 340° C. or higher under pressure. Arepeating structural unit and its constitutional ratio of liquid crystalpolyester A-1 are as follows.

(1-2) (B) Copolymer having reactivity with liquid crystal polyesterconstituting liquid crystal polymer exhibiting optical anisotropy atmelting

According to the method described in Example 5 of JP-A No. 61-127709, arubber of methyl acrylate/ethylene/glycidyl methacrylate=59.0/38.7/2.3(ratio by weight) and a Mooney viscosity=15 was obtained. Hereinafter,the rubber is abbreviated as B-1 in some cases.

Herein, a Mooney viscosity is a value measured using a 100° C. largerotor according to JIS K6300. In addition, a melting heat was measuredfor 10 mg of a sample at a scanning temperature of 10° C./min usingDSC-50 manufactured by Shimadzu having a sensitivity of 0.01 J/g. Amelting point could not be detected, and a melting heat could not bemeasured.

(2) Aramid Paper

A commercially available P-aramid pulp (Twaron 1094 manufactured by AkzoNobel K. K., specific surface area 4.55 m²/g, filtered water degree 683ml) as a single material was subjected to wet paper making at a weightof 37 g/m² by a conventional method, and passed through a calendar rollset at 280° C. at a linear pressure of 25 kg/cm to obtain an aramidpaper. A thickness of this aramid paper was 55 μm. A torn length was0.57 km. A moisture absorption rate was 4.5%. In addition, a Coefficientof thermal expansion measured at 50° C. to 150° C. by a TMA method was3×10⁻⁶/° C. in both of a MD direction and a TD direction. The aramidpaper is called P-1 in some cases.

EXAMPLE 1

At a blending ratio of 82 parts by weight of A-1 and 18 parts by weightof B-1, melting and kneading was performed at a cylinder set temperatureof 350° C. under a screw rotation number of 450 rpm using a TEX-30 typebiaxial extruder manufactured by The Japan Steel Works, Ltd. to obtain acomposition in which A-1 is a continuous phase, and B-1 is a dispersionphase. This composition pellet exhibited optical anisotropy at 340° C.or higher under pressure, and a flowing temperature was 328° C. Theresulting composition is called C-1 in some cases.

C-1 was melted and extruded at a cylinder set temperature of 350° C.under a screw rotation number of 60 rpm using a 60 mmφ monoaxialextruder equipped with a cylinder die, a melted resin was extrudedupwardly from a cylindrical die of a diameter 50 mm, a lip interval 1.0mm and a die set temperature 348° C., the dried air was pressed in ahollow part of the resulting cylindrical film, this was inflated,cooled, and passed through a nip roll to obtain a film. A blowing ratiowas 2.5, a drawing down ratio was 16, and an actually measured averagethickness of a film was 25 μm. A water stream permeability of the filmwas 0.4 (g/m²·24 hr), and a water absorption rate was better as 0.05%.In addition, a tensile elastic modulus in a MD direction was 3400kgf/mm, and a breakage elongation was 2% or smaller.

A normally used heat resistant temperature was 170° C. A solder heatresistance temperature was 285° C. In addition, a surface free energy ofthe film was 40 dyne/cm.

Further, a Coefficient of thermal expansion measured at 50° C. to 150°C. by a TMA method was −20×10⁻⁶/° C. in a MD direction, and 30×10⁻⁶/° C.in a TD direction, and anisotropy was recognized. The film is called F-1in some cases.

P-1 and F-1 were overlaid in an order of (I) F-1, (II) P-1 and (III)F-1, and this was passed through a calendar roll set at 325° C. (atemperature of a flowing temperature of C-1 minus 3° C.) at a linearpressure of 25 kg/cm to obtain a laminate L-1 having an average actuallymeasured thickness of 77 μm. A water absorption rate of L-1 was betteras 0.8%. When the laminate was immersed in a solder bath regulated at280° C. for 10 seconds, deformation was not recognized, and appearancewas also better.

A Coefficient of thermal expansion measured at 50° C. to 150° C. by aTMA method was 3×10⁻⁶/° C. in both of a MD direction and a TD direction,and anisotropy was not recognized.

EXAMPLE 2

P-1 and F-1 obtained in Example 1, and electrolytic copper foil M-1 of athickness of 18 μm were overlaid in an order of (i) to (v) such as (i)M-1, (ii) F-1, (iii) P-1, (iv) F-1 and (v) M-1, and passed through acalendar roll set at 325° C. (a temperature of a flowing temperature ofC-1 minus 3° C.) at a linear pressure of 50 kg/cm to obtain a laminateL-2 having an average actual measured thickness of 112 μm. A simplecircuit having a copper foil residual area rate of 20% was made on acopper foil on both surfaces of L-2 by conventional etching treatment toobtain a double-sided circuit substrate B-1. A water absorption rate ofB-1 was better as 0.8%. In addition, the substrate was immersed in asolder bath adjusted at 280° C. for 10 seconds and deformation was notrecognized, and appearance was also better. In addition, after immersionin a solder bath, breakage of a circuit is not recognized.

COMPARATIVE EXAMPLE 1

According to the same manner as that of Example 1 except that acommercially available PET film having a thickness of 25 μm (ToyoboEspet) was used in place of F-1, a temperature of calendar roll was 250°C., and a linear pressure was 80 kg/cm, a laminate R-1 having an averageactually measured thickness of 78 μm was obtained. A water absorptionrate of R-1 was 1.6%, therefore, this can not be said to be better. Inaddition, when the laminate was immersed in a solder bath adjusted at280° C. for 10 seconds, it was greatly deformed.

COMPARATIVE EXAMPLE 2

According to the same manner as that of Example 2 except that acommercially available PET film having a thickness of 25 μm (ToyoboEspet) was used in place of F-1, a temperature of a calendar roll was250° C., and a linear pressure was 100kg/cm, a laminate R-2 having anaverage actually measured thickness of 116 μm was obtained. A simplecircuit having a copper foil residual area rate of 20% was made on acopper foil of both surfaces of R-2 by conventional etching treatment toobtain a double-sided circuit substrate R-3. A water absorption rate ofR-3 was 1.6%.

In addition, when the laminate was immersed in a solder bath adjusted at280° C. for 10 seconds, it was greatly deformed, and breaking of a wireof a part of a circuit was recognized.

According to the present invention, an aramid laminate which isexcellent in solder heat resistance and low hygroscopicity and haslittle anisotropy can be obtained.

1. A process for preparing an aramid laminate, which comprisesimpregnating a surface and an interior of an aramid paper with a liquidcrystal polymer, and laminating a layer comprising an araimd paper and alayer comprising a liquid crystal polymer.
 2. The process for preparingan aramid laminate according to claim 1, wherein the liquid crystalpolymer is a liquid crystal polyester resin composition in which (A)liquid crystal polyester is a continuous phase and (B) a copolymerhaving a functional group having reactivity with liquid crystalpolyester is a dispersion phase.
 3. The process for preparing an aramidlaminate according to claim 2, wherein the liquid crystal polyesterresin composition is a composition comprising 56.0 to 99.9% by weight of(A) liquid crystal polyester, and 44.0 to 0.1% by weight of (B) acopolymer having a functional group having reactivity with liquidcrystal polyester.
 4. The process for preparing an aramid laminateaccording to claim 1, wherein a layer comprising an aramid paper and alayer comprising a liquid crystal polymer are thermally fused in atemperature range of a temperature lower than a flowing temperature of aliquid crystal polymer by 30° C. to lower than 400° C.
 5. The processfor preparing an aramid laminate according to claim 4, wherein thermalfusing is performed at a pressure of a planar pressure of 10 kg/cm² orhigher or a linear pressure of 20 kg/cm or higher.
 6. The process forpreparing an aramid laminate according to claim 1 or 2, wherein anaramid paper and a liquid crystal polymer-film are thermally fused.
 7. Acircuit substrate characterized by comprising an aramid laminateaccording to claim 1.